Co-feeding studies of ticks infected with Anaplasma marginale

Ticks often cluster at preferred feeding sites on hosts, and the co-feeding of ticks at the same site has been shown to increase feeding success and the transmission of some pathogens. While the major route of infection of ticks with pathogens is via the bloodmeal during feeding on a parasitemic host, non-systemic transmission of viruses and spirochetes has been shown to occur from infected to uninfected ticks at common feeding sites on uninfected hosts. In this research, two separate studies were done using the tick-borne rickettsial pathogen of cattle, Anaplasma marginale. In one study we tested whether A. marginale could be transmitted non-systemically from infected to uninfected Dermacentor variabilis males while co-feeding on rabbits. Infection of ticks was determined by allowing them to transmission feed on susceptible cattle and by DNA probe and microscopy studies on salivary glands. In the second study, we tested whether the co-feeding of male and female ticks on parasitemic cattle would increase the acquisition and development of A. marginale in males. A. marginale infections in salivary glands were determined by quantitative PCR after the ticks were allowed to transmission feed on susceptible cattle. Non-systemic transmission of A. marginale did not occur from infected and uninfected ticks that fed at the same site on rabbits and, therefore, does not appear to be a means of A. marginale transmission. A. marginale infections in male ticks were not increased while co-feeding with females. Thus, co-feeding of adult Dermacentor spp. does not appear to influence the dynamics of A. marginale transmission.